Modulator

Abstract

A low frequency signal generating portion 1 generates a first discrete signal (a signal sampled at a first sampling rate f1). A band pass portion 2 operates at a second sampling rate f2, performs a frequency selecting operation to a second discrete signal generated when the first discrete signal generated by the low frequency signal generating portion 1 is inputted, and generates a modulated signal with a prescribed center frequency.

What is claimed is:  
     
       1. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means comprising an IIR filter, wherein said IIR filter operates at said second sampling rate and executes said band selection.  
     
     
       2. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means comprising a leapfrog IIR filter, wherein said leapfrog IIR filter operates at said second sampling rate and executes said band selection.  
     
     
       3. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means comprising a FIR filter, wherein said FIR filter operates at said second sampling rate and executes said band selection.  
     
     
       4. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal, said discrete signal generating means comprising a low pass filter, operating at said first sampling rate, for passing only a signal which exists at low frequencies; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means including an IIR filter or a FIR filter, and said low pass filter has a frequency pass characteristic capable of compensating for a frequency pass characteristic of said IIR filter or said FIR filter.  
     
     
       5. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal, said discrete signal generating means comprising:  
       a low pass filter for passing only a low frequency signal, and  
       an interpolating filter for interpolating said low frequency signal passed by said low pass filter at said first sampling rate; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means including an IIR filter or a FIR filter, and said low pass filter has a frequency pass characteristic of said IIR filter or said FIR filter.  
     
     
       6. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal, said discrete signal generating means comprising:  
       a low pass filter, operating at said first sampling rate, for passing only a low frequency signal,  
       trigonometric function generating means for generating a trigonometric function with a prescribed frequency, and  
       multiplying means for multiplying said low frequency signal from said low pass filter by said trigonometric function generated in said trigonometric finction generating means; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means including an IIR filter or a FIR filter, and said low pass filter has a frequency pass characteristic capable of compensating for a frequency pass characteristic of said IIR filter or said FIR filter.  
     
     
       7. A device comprising: 
       discrete signal generating means for sampling a transmission signal inputted from an outside source at a first sampling rate and generating a discrete signal, said discrete signal generating means comprising:  
       a low pass filter for passing only a low frequency signal,  
       an interpolating filter for interpolating said low frequency signal from said low pass filter at said first sampling rate,  
       trigonometric function generating means for generating a trigonometric function with a prescribed frequency, and  
       multiplying means for multiplying said low frequency signal which has been interpolated by said interpolating filter by said trigonometric function generated in said trigonometric function generating means; and  
       band passing means, operating at a second sampling rate which is higher than said first sampling rate, for executing a band selection by passing a portion of said discrete signal which exists in a prescribed frequency band, wherein said prescribed frequency band of said band passing means has a center frequency which is not zero and said portion of said discrete signal is an aliasing component of said discrete signal, said band passing means including an IIR filter or a FIR filter, and said low pass filter has a frequency pass characteristic capable of compensating for a frequency pass characteristic of said IIR filter or said FIR filter.